1. Field of the Invention
The present invention relates to an image sensor chip package and a method for fabricating the same. More specifically, the present invention relates to an image sensor chip package having no wire bonds and a fabrication method thereof, thus enabling production of further miniaturized and thinned packages.
2. Description of the Related Art
Conventionally, an image sensor is comprised of a semiconductor device that can transform an optical image into an electric signal. Such an image sensor is used for storage, transmission and display of an image signal. Semiconductor image sensors are generally classified into Charge-Coupled Device (CCD) and Complementary Metal Oxide Semiconductor (CMOS) image sensors. In a CCD image sensor, charges are transmitted in a desired direction by controlling the depth of potential wells. A CMOS image sensor includes one or more transistors and photodiodes as an optical sensor in one pixel.
A CCD image sensor has less susceptibility to noise and higher image qualities in comparison with CMOS image sensors. Accordingly, a CCD image sensor is applicable for high quality image devices such as a digital camera. On the other hand, a CMOS image sensor has low power consumption and low production cost in comparison with a CCD image sensor. In addition, a CMOS image sensor generally incorporates peripheral circuits. This is especially advantageous because CMOS image sensors may be produced by a general semiconductor device (e.g., CMOS) manufacturing technology. A CMOS image sensor is applicable for a camera attached to a personal digital assistant (PDA) or cellular phone. Because of the rapid progress of its manufacturing technology, CMOS image sensors have been used in a variety of applications.
Generally, an image sensor chip package is fabricated or packaged by attaching a transparent substrate to one surface of a chip (on which a sensing element is formed), and attaching a separate substrate to the other surface of the chip. The transparent substrate is generally used for receipt of light and protection of the chip. CLCC (Ceramic Leadless Chip Carrier), PLCC (Plastic Leadless Chip Carrier), COB (Chip on Board) and the like are used for packaging such an image sensor chip.
FIG. 1 shows an image sensor chip package fabricated by the CLCC packaging method. Referring to FIG. 1, a chip 102 is attached to a blank package 100 formed of ceramic material with an adhesive 104. The chip 102 is electrically connected to leads 108 disposed in the package 100 by gold (Au) or aluminum (Al) wires 106. Then, in order to protect the chip 102 and enable a sensing element 110 thereon to receive light, a transparent substrate 120 is attached on the top of the package 100.
Drawbacks of CLCC packages include limited numbers of leads and high cost. In the case of a CLCC chip package, a package is formed of ceramic material, which may limit the number of leads. In addition, due to the high price of ceramic packages, the CLCC chip package is not preferred for highly-integrated chips. In a PLCC chip package, a chip is attached to a blank package with an adhesive, and chip pads are electrically connected to leads inside the package with Au or Al wires. Then, for the protection of the chip and the receipt of a light, a transparent substrate is attached and sealed on the top of the package. A PLCC chip package may be fabricated by a conventional plastic package fabricating method. That is, a chip is attached to a lead frame pad with an adhesive, and then the chip and the lead frame are electrically connected to each other by wires. Further, epoxy molding compound (EMC) envelops the outside of the chip and the lead frame, except the upper surface of the chip. Then, a transparent substrate is attached and sealed on the upper surface of the chip. Finally, the package is completed through a trimming process, forming process and marking process on the lead frame.
However, such a PLCC chip package may develop a micro-gap between the epoxy molding compound and the transparent substrate due to a difference in material properties between the organic material and the inorganic material. In addition, the epoxy molding compound in a PLCC chip package does not block alpha particles, which can result in electrical failures of the image sensor element. As a result, the reliability of the PLCC package may be less than optimal.
Recently, COB packaging technology has been developed as a method for modularizing an image sensor chip package, using an anisotropic conductive film (ACF). ACF has also been also used in manufacturing liquid crystal display (LCD) panels. Korean Patent Laid-Open Publication No. 2003-69321 discloses a method for fabricating an image sensor chip package, which utilizes a Flip Chip Au bumping process and COB packaging technology.
According to the COB packaging technology, a chip is attached on a substrate provided with a predetermined pattern, and an electrode pad on the chip is electrically connected to the predetermined pattern with wires. Then, a transparent substrate is attached on the top of the chip, thus protecting the chip. However, such a COB chip package is modularized using a housing and a lens right after the chip is attached. Therefore, it may result in failures due to contamination of impurities.